1. Field of the Invention
This invention concerns an improved synchromesh gearbox which uses less energy than conventional gearboxes in a direct drive mode. More particularly, the gearbox hereof includes an countershaft carrying one or more change-speed gears which can be operatively decoupled from the gearbox input shaft when the gearbox is placed in a direct drive mode.
2. Description of the Prior Art
Of the types of power transmissions used in modern automobiles, synchromesh gearboxes are regarded as being among the most efficient and easiest to use. As a result, they are commonly employed in virtually all automotive applications such as, for example, passenger automobiles and trucks. The evolution of the synchromesh gearbox has avoided many of the problems of conventional gearboxes such as gear wear and the necessity of double-clutching.
Both conventional and synchromesh gearboxes include an input shaft which receives power from an engine, an output shaft, which transfers power to the driven wheels, and a layshaft or countershaft, which includes a number of change-speed gears. The countershaft is coupled to the input shaft by a countershaft input gear which meshes with and is driven by an input gear on the main shaft. Using a four-speed gearbox as an example, 1st, 2nd and 3rd gears are of a higher gear ratio, so that the input shaft turns more rapidly than does the output shaft in these gears. However, in 4th gear, the input shaft is directly coupled to the output shaft so that the input shaft turns at the same speed as the output shaft. When operating in 4th gear, or a direct-drive mode, no power is actually transmitted to the output shaft through the countershaft.
Notwithstanding the absence of any power transmission through the countershaft, synchromesh and conventional gearboxes drive the countershaft because the countershaft input gear is fixed to the countershaft and driven by the input gear of the input shaft. Because the countershaft is typically immersed in 90 weight SAE gearbox lubricant, a substantial amount of energy is consumed just in turning the countershaft and its gears. In fact, it is estimated that about one to ten horsepower of the power input into the gearbox is used in turning the countershaft when in a direct drive mode at normal highway speeds. This energy consumption is analogous to a fan blade pushing the lubricant as well as an oil pump where the highly viscous gearbox lubricant is forced between meshing teeth and produces no benefit when the gearbox is in a direct drive mode. If even a portion of this power loss can be avoided, a substantial improvement in overall performance and fuel economy of the automobile can be obtained.
It is thus an object of the present invention to present a practical solution to the problem of wasted power consumed by the countershaft when the engine is operating in a direct drive mode.
It is another object of this invention to develop a gearbox which can be used in virtually all automotive applications.
It is another object of this invention to develop a gearbox which can be substituted in size and application for a typical synchromesh gearbox without substantial additional cost.
It is another object of this invention to develop a gearbox which is readily adapted to use both in passenger cars and light trucks.
It is another object of this invention to develop a gearbox which is useful for racing applications.